Remove redundant material_ prefix

These files are already in the "material" folder. They don't need to be
prefixed with material again.

Fixes #702

packages/flutter/lib/material.dart

@@ -7,7 +7,9 @@
 /// See https://www.google.com/design/spec/material-design/introduction.html
 library material;
 
+export 'src/material/app.dart';
 export 'src/material/bottom_sheet.dart';
+export 'src/material/button.dart';
 export 'src/material/card.dart';
 export 'src/material/checkbox.dart';
 export 'src/material/chip.dart';
@@ -33,11 +35,9 @@ export 'src/material/icon_theme.dart';
 export 'src/material/icon_theme_data.dart';
 export 'src/material/ink_well.dart';
 export 'src/material/input.dart';
+export 'src/material/list.dart';
 export 'src/material/list_item.dart';
 export 'src/material/material.dart';
-export 'src/material/material_app.dart';
-export 'src/material/material_button.dart';
-export 'src/material/material_list.dart';
 export 'src/material/page.dart';
 export 'src/material/popup_menu.dart';
 export 'src/material/progress_indicator.dart';

packages/flutter/lib/src/material/dialog.dart

@@ -6,8 +6,8 @@ import 'dart:async';
 
 import 'package:flutter/widgets.dart';
 
+import 'button.dart';
 import 'colors.dart';
-import 'material_button.dart';
 import 'material.dart';
 import 'theme.dart';
 

packages/flutter/lib/src/material/flat_button.dart

@@ -4,7 +4,7 @@
 
 import 'package:flutter/widgets.dart';
 
-import 'material_button.dart';
+import 'button.dart';
 import 'theme.dart';
 
 /// A material design "flat button".

packages/flutter/lib/src/material/raised_button.dart

@@ -4,8 +4,8 @@
 
 import 'package:flutter/widgets.dart';
 
+import 'button.dart';
 import 'colors.dart';
-import 'material_button.dart';
 import 'theme.dart';
 
 /// A material design "raised button".

packages/flutter/lib/src/material/snack_bar.dart

@@ -4,11 +4,11 @@
 
 import 'package:flutter/widgets.dart';
 
+import 'button.dart';
 import 'flat_button.dart';
 import 'material.dart';
-import 'material_button.dart';
-import 'theme.dart';
 import 'theme_data.dart';
+import 'theme.dart';
 import 'typography.dart';
 
 // https://www.google.com/design/spec/components/snackbars-toasts.html#snackbars-toasts-specs

packages/flutter/lib/src/material/two_level_list.dart

@@ -6,8 +6,8 @@ import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
 import 'icon.dart';
+import 'list.dart';
 import 'list_item.dart';
-import 'material_list.dart';
 import 'theme.dart';
 import 'theme_data.dart';